Gas sensors are known and have been used to sense various gases such as hydrogen, carbon monoxide, carbon dioxide and the like. While known gas sensors are useful and effective for their intended purpose, it has been recognized that at times they can lose sensitivity over time. For example, in connection with electrochemical-type gas sensors, such sensors incorporate a catalytic electrode which is used in connection with detecting gas within the sensor. The activity of that electrode tends to be reduced gradually over time due to contamination and poisoning of the structure. Consequently, the sensitivity of the associated sensor tends to decrease or drift downward. As a result, it is desirable to be able to calibrate such sensors from time to time.
Structures which can generate calibration gases are of interest and have been developed. One such structure is disclosed in previously filed U.S. patent application Ser. No. 10/856,363 filed May 28, 2004, now U.S. Pat. No. 7,037,368, for Calibration Device For Gas Sensors. That application has been assigned to the Assignee hereof and is hereby incorporated by reference. Another such structure has been disclosed in U.S. patent application Ser. No. 10/908,737 previously filed on May 24, 2005, now U.S. Pat. No. 7,174,766, entitled “Calibration Device For Carbon Dioxide Sensor”. That application has been assigned to the Assignee hereof and is hereby incorporated by reference.
Beyond an apparatus and a method for generating calibration gas, there continues to be a need for gas sensors which can readily and conveniently calibrated. Preferably such units could be substantially self-contained. It would also be preferable if such units could incorporate a self-calibrating capability without significantly adding to the manufacturing costs, size or weight of such units, especially portable gas detectors.